There is currently an unprecedented focus on the performance of propeller-based marine vehicles with particular emphasis on greater acceleration and higher top speeds. Marine vehicle owners and operators, in general, seek to increase the performance of their vehicle through tuning or modifications. A vehicle's propeller determines many performance characteristics.
Acceleration and top speed are dependent on many factors including, for instance, the power generated by the motor, the efficiency of the drive train, and the design of the hull. A consumer will typically study each of these factors when shopping for a vehicle. Once the marine vehicle is purchased, these factors are largely unchangeable or are cost-prohibitive to change.
A propeller-driven marine vehicle's performance is also largely dictated by the design and implementation of the propeller hub and propeller blades. It is thought that the propeller hub and blades are much easier to modify and upgrade than motors, drive trains and hulls.
Typically, propeller systems employ inboard or outboard motors with a drive shaft connecting the motor to a propeller hub. The drive shaft rotates the propeller hub, which in turn rotates one or more propeller blades that are formed as a part of the hub. The performance specifically attributed to the propeller hub and blades is derived from a number of factors, such as the shape of the blades, the presence of exhaust gases at the surface of the blades, the length of the outer hub, and the number of blades. Certain blade shapes provide high acceleration but low top speeds or poor mid-range acceleration while other blades might be constructed to provide just the opposite. Also, commercially available propeller hubs only contemplate propeller blades that are identically shaped. The performance of mixed-shape blade sets has not been considered. A means to selectively modify the dimensions of the propeller outer hub to affect the exit point of exhaust gases is also thought to be unknown in the prior art.
Exhaust gases produced by the motor are typically directed through the hub and, therefore, exit behind the propeller blade(s) when the marine vehicle is moving forward. Gas is much easier to displace than water. It follows then that when the blades contact gas bubbles or a gas stream the resistance to rotation is reduced, and the motor can more efficiently spin the propeller hub. Of course, at the points that the blades are in contact with gas bubbles, the blades are not displacing water, which is what propels the boat forward. It is possible for excessive gas bubbles or a gas stream to cause the propeller blades to “break loose.” This effect is not unlike a motor vehicle spinning its tires when the acceleration force on the tires exceeds the tires' maximum surface grip. Basically, it becomes easier for the motor to spin the tires once the breaking point has been reached but acceleration suffers. The same basic principle can be applied to marine propellers.
Propeller and boat builders have been known to try to find a medium between facilitating the rotation of the propeller at low speeds while maximizing acceleration. As such, exhaust gases have been known to be purposefully introduced to the blade surfaces by providing exhaust ports upstream of the blades.
The length of the outer hub also plays a role. With short propeller outer hubs, the exhaust gases exit the hub in such a way as to interact with the surfaces of the blades. Longer outer hubs can reduce or eliminate this interaction. Because all of the above performance factors are largely interrelated, the ideal outer hub length can vary between boats. Some boats will perform better with longer outer hubs than others, and vice versa. Currently, a boat owner can only modify this aspect of their vehicles performance by replacing the propeller.
There is a need for an apparatus and method to readily adjust the length of a propeller outer hub without actually replacing the propeller altogether. In addition, consumers desire a propeller hub with blade sets that provide distinct geometries in order to increase the propeller's performance characteristics across the propeller's operating range. An adjustable length propeller outer hub and propeller blade sets with distinct geometries in accordance with the present invention provide new propeller tuning and modification options.